It is the long range purpose of this project to make clinically available a radio-labelled fibrinogen leg scanning technique as a screening test to detect lower extremity venous thrombosis. This technique will be used both as a diagnostic procedure and in expectant scanning of high risk patients. The first phase of this project was to prepare 125I-labelled fibrinogen and compare two different methods of preparation. The chloramine-T method was compared to chemical conjugation to a 125I-containing acylating agent method (Bolton and Hunter). The newer Bolton and Hunter technique was found to be unsatisfactory for labelling human fibrinogen. The second phase of this project will require intravenos injection of 100uCi of 125I-fibrinogen into selected patients. We expect to detect venous thrombosis in the lower extremities. This will allow investigation of the course of thrombosis, its relationship to various disease states and early initiation of treatment which will hopefully decrease the incidence of pulmonary embolism.